One known type of information storage device is a disk drive device that uses magnetic media to store data and a movable read/write head that is positioned over the media to selectively read from or write to the disk.
Consumers are constantly desiring greater storage capacity for such disk drive devices, as well as faster and more accurate reading and writing operations. Thus, disk drive manufacturers have continued to develop higher capacity disk drives by, for example, increasing the density of the information tracks on the disks by using a narrower track width and/or a narrower track pitch. However, each increase in track density requires that the disk drive device have a corresponding increase in the positional control of the read/write head in order to enable quick and accurate reading and writing operations using the higher density disks. As track density increases, it becomes more and more difficult using known technology to quickly and accurately position the read/write head over the desired information tracks on the storage media. Thus, disk drive manufacturers are constantly seeking ways to improve the positional control of the read/write head in order to take advantage of the continual increases in track density.
One approach that has been effectively used by disk drive manufacturers to improve the positional control of read/write heads for higher density disks is to employ a secondary actuator, known as a micro-actuator, that works in conjunction with a primary actuator to enable quick and accurate positional control for the read/write head. Disk drives that incorporate micro-actuators are known as dual-stage actuator systems.
Various dual-stage actuator systems have been developed in the past for the purpose of increasing the access speed and fine tuning the position of the read/write head over the desired tracks on high density storage media. Such dual-stage actuator systems typically include a primary voice-coil motor (VCM) actuator and a secondary micro-actuator, such as a PZT element micro-actuator. The VCM actuator is controlled by a servo control system that rotates the actuator arm that supports the read/write head to position the read/write head over the desired information track on the storage media. The PZT element micro-actuator is used in conjunction with the VCM actuator for the purpose of increasing the positioning access speed and fine tuning the exact position of the read/write head over the desired track. Thus, the VCM actuator makes larger adjustments to the position of the read/write head, while the PZT element micro-actuator makes smaller adjustments that fine tune the position of the read/write head relative to the storage media. In conjunction, the VCM actuator and the PZT element micro-actuator enable information to be efficiently and accurately written to and read from high density storage media.
One known type of micro-actuator incorporates PZT elements for causing fine positional adjustments of the read/write head. Such PZT micro-actuators include associated electronics that are operable to excite the PZT elements on the micro-actuator to selectively cause expansion and/or contraction thereof. The PZT micro-actuator is configured such that expansion and/or contraction of the PZT elements causes movement of the micro-actuator which, in turn, causes movement of the read/write head. This movement is used to make faster and finer adjustments to the position of the read/write head, as compared to a disk drive unit that uses only a VCM actuator. Exemplary PZT micro-actuators are disclosed in, for example, JP 2002-133803; U.S. Pat. Nos. 6,671,131 and 6,700,749; and U.S. Publication No. 2003/0168935, the contents of each of which are incorporated herein by reference.
FIG. 1a illustrates a conventional disk drive unit and show a magnetic disk 101 mounted on a spindle motor 102 for spinning the disk 101. A voice coil motor arm 104 carries a head gimbal assembly (HGA) that includes a micro-actuator 105 with a slider incorporating a read/write head 103. A voice-coil motor (VCM) is provided for controlling the motion of the motor arm 104 and, in turn, controlling the slider to move from track to track across the surface of the disk 101, thereby enabling the read/write head 103 to read data from or write data to the disk 101.
Because of the inherent tolerances (e.g., dynamic play) of the VCM and the head suspension assembly, the slider cannot achieve quick and fine position control, which adversely impacts the ability of the read/write head to accurately read data from and write data to the disk when only a servo motor system is used. As a result, a PZT micro-actuator 105, as described above, is provided in order to improve the positional control of the slider and the read/write head 103. More particularly, the PZT micro-actuator 105 corrects the displacement of the slider on a much smaller scale, as compared to the VCM, in order to compensate for the resonance tolerance of the VCM and/or head suspension assembly. The micro-actuator enables, for example, the use of a smaller recording track pitch, and can increase the “tracks-per-inch” (TPI) value for the disk drive unit, as well as provide an advantageous reduction in the head seeking and settling time. Thus, the PZT micro-actuator 105 enables the disk drive device to have a significant increase in the surface recording density of the information storage disks used therein.
FIGS. 1b-d are various views of a typical PZT micro-actuator and support structure. In particular, FIG. 1b is an exploded partial perspective view of a PZT element micro-actuator and support arm, FIG. 1c is a top view of the PZT element micro-actuator and support arm of FIG. 1b, and FIG. 1d is a side view of the PZT element micro-actuator and support arm of FIG. 1b. According to the techniques disclosed in U.S. Publication No. 2003/0168935, a slider 103 having a read/write sensor is partially mounted on the slider support 121 of the suspension. A bump 127 is formed on the slider support 121 to support the center of the back surface of the slider. A flex cable 122 with multiple traces operably couples the slider support 121 and a metal base flexure parts 123. A suspension load beam 124 with a dimple 125 supports the slider support 121 and flexure parts 123. The slider 103 is partially mounted on the top of the flexure 107. The dimple 125 of the suspension load beam supports the bump 127 of the slider support, which keeps the load force from the load beam 124 applied to the center of the slider when the head is flying over the disk. There are two thin-film PZT pieces 10 attached to the tongue region 128 of the suspension and is at least partially underneath the slider. A parallel gap 111 exists between the back side of the slider and the top surface of the PZT element. When a voltage is applied to the thin film PZT pieces 10, one of the two PZT pieces may contract (as shown by arrows D), and the other side may expand (as shown by arrows E). This generates a rotation torque with respect to the slider support (as shown by arrow C). Because the slider 103 is partially mounted on the slider support 121 and the bump 127, a parallel gap 111 exists between the slider and the thin-film PZT elements.
Normally, the slider will rotate against the dimple 125. Unfortunately, when a vertical vibration or other shock occurs (e.g. when a “tilt-drop” shock occurs), the slider is rotated against the dimple and the leading edge of the slider may hit the PZT element. The PZT element may suffer damage, such as, for example, a crack or a break. This arrangement thus raises reliability concerns, for example, with respect to the PZT elements.
FIG. 1e, which is a side-view of the tongue area of the HGA during a shock, demonstrates this problem. In particular, the slider rotates against the dimple. Its leading edge tilts, and it comes into contract with the thin-film PZT element 10 in the region 130. This contact, brought about by the occurrence of a shock for example, may damage the thin-film PZT element. For example, because the edge portion of the slider 103 is sharp, the region 130 in the PZT element surface may crack or become scratched, especially because it formed from, for example, a thin-film material. Accordingly, the PZT element will be damaged.
Thus it will be appreciated that there is a need in the art for micro-actuators, head gimbal assemblies, disk drives, and methods for making the same that overcome one or more of these and/or other disadvantages.